Enhancement of antigen immunogenicity

ABSTRACT

A new method is described for eliciting IgG antibody response to proteins or synthetic peptides, particularly those that are weakly immunogenic, without the requirement for the use of adjuvants, thereby making it easier and safer to confer protection against pathogenic organisms. The antigen is coupled to a monoclonal antibody, specific for membrane determinants expressed on certain types of mammalian recipient cells, called antigen presenting cells. The monoclonal antibody acts as a &#34;vector&#34; or &#34;delivery vehicle&#34; for targeting foreign antigens onto such recipient cells. This targeting facilitates subsequent antigen recognition by helper T-cells, which are pivotal in helping the induction of antigen-specific IgG responses.

REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part to copending U.S. patent application Ser. No. 046,095 filed May 5, 1987, now U.S. Pat. No. 4,950,480.

FIELD OF INVENTION

The present invention relates to a novel procedure for immunization against disease, and/or the generation of antibody responses in vivo without the use of adjuvents and to novel vaccine materials and conjugates used in the procedure.

BACKGROUND OF THE INVENTION

In the conventional method of protection against disease by vaccination, the central principle involves the injection or ingestion of a material that will elicit antibodies against said material, such that when challenged alter with a pathogenic organism containing homologous material, the individual to whom the material has been administered is protected against the pathogenic disease. The material injected or ingested that have this property of eliciting antibodies are called antigens.

It has been known for many years that the immunogenicity (that is, its ability to elicit antibodies) of an antigen can be improved by the addition of so-called adjuvants. In some cases, materials that apparently have little or no immunogenicity have been made to make high titres of antibody in in vivo systems by the addition of an adjuvant. Some of these adjuvants re, however, highly toxic and can cause undesirable side effects or lesions. Aluminum hydroxide or aluminum phosphate are routinely used as adjuvant for human vaccines, but have been known to cause lumps at the site of injection. Freund's complete adjacent (FCA), a mixture of a light petroleum oil and killed Mycobacterium tuberculosis, can often produce excellent titres for materials which do not normally give antibodies in vivo under any other conditions. Unfortunately lesions will often develop at the site of injection when using this material, making the procedure unacceptable for human use.

There are a number of other materials which have been investigated for use as adjuvants. In published European patent Application No. 0149581, the use of muramyl di-peptide is disclosed. In published United Kingdom Patent Application No. 2,053,231, the use of a synthetic adjuvant consisting of tetrapeptides or pentapeptides is disclosed. In earlier patents, the use of oil emulsions is disclosed as having an adjuvanting effect. Unfortunately, it appears that the better a material is at behaving as an adjuvant to antigen immunogenicity, the worse are the side effects. For example, it has been shown that muramyl dipeptide is an excellent adjuvant but appears to have a number of undesirable properties which prevent its use in human vaccines.

In general, all the adjuvants presently in use in mammals fall into two distinct types. The first type involves the so-called "depot" effect and the second type depends on general immunological stimulation of the system under study. The adjuvants which rely on the depot effect are believed to bring the immune cells to the antigen site, where the depot effect relies on the injected antigen being trapped or insolubilized in a medium, giving sustained circulating levels. The second type of adjuvant, involving general stimulation of the immune system, appears to relay on an inflammatory reaction resulting in a series of cells being stimulated, such that any antigen has an improved chance of eliciting antibodies.

Current theories of immunology suggest that, in order to provide a potent antibody response, an antigen must be seen by both B cells, which subsequently develop into the antibody producing cells, and also by helper T-cells, which provide growth and differentiation signals to the antigen specific B-cells. Helper T-cells recognize the antigen on the surface of antigen-presenting cells (APC) in association with Class II major histomcompatibility complex (MHX) gene products.

SUMMARY OF INVENTION

The present invention involves a new method of immunization which does not involve the use of unacceptable adjuvants. The present invention, in one aspect, provides a novel immunization method and takes advantage of the fact that both B-cells and APC of the macrophage lineage express Class II MHC gene products. Instead of injecting antigen in the presence of adjuvant, the antigen is coupled to a monoclonal antibody specific for a surface structure of antigen-presenting cells, including Class II MHC determines, and is injected in this form. By coupling it to the antigen, the monoclonal antibody is converted into a "vector" or "delivery vehicle" for targeting the antigen onto the relevant cells in the immune system. In effect, the method brings the antigen to the antigen-presenting cells rather than the other way around, as is thought to be the case when antigen is injected in the presence of Freund's complete adjuvant.

The present invention also provides, in another aspect, a novel vaccine for utilization in the novel immunization method comprising a conjugate of an antigen and a monoclonal antibody specific for a gene product of the major histocompatibility complex or other surface structure of antigen-presenting cells in a suitable carrier medium. The present invention, in a further aspect, provides the novel conjugate.

The present invention provides a new method of enhancing the immunogenicity of weak antigens, which does not involve the use of unacceptable adjuvants, is therefore much safer and can utilize materials that are not normally very antigenic. An example of such materials are small peptides which are epitopes of larger proteins or are protein subunits of the pathogens themselves. Epitopes are parts of a larger antigen which represent the immunological recognition sites within the structure. The vaccination method of the invention, therefore, can avoid the injection of killed or attenuated organisms, which can have unfortunate side effects, by the use of such epitopes or protein subunits in the form of conjugate with targeting monoclonal antibodies.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1 contains graphical representations, labelled A to D, of the anti-avidin responses in mice in one series of experiments described in Example II below, with FIG. 1A showing the response in (B6×C3H)F1 mice (open circles) and B6 mice (closed circles) to (anti-I-A^(k))-avidin conjugate, FIG. 1B slowing the response in such mice to a mixture of avidin and unmodified anti-I-A^(k) MAb, FIG. 1C showing the response in such mice to a conjugate of avidin to a control anti-NP MAb, and FIG. 1D showing the response in such mice to avidin adjuvanted with Freund's Complete Adjuvant;

FIG. 2 is a graphical representation of secondary anti-avidin responses in mice in another series of experiments described in Example II below. showing the response in (B6×C3H)F1 mice (open squares) and B6 mice (closed squares) to (anti-IE^(k)) avidin conjugate;

FIG. 3 contains graphical representations of anti-bovine serum albumin responses in mice in a further series of experiments described in Example III below, showing the response in (B6×C3H)F1 mice (open circles) and B6 mice (closed circles) to a conjugate of anti-I-A^(k) antibody, avidin and bovine serum albumin;

FIG. 4 contains a graphical representations of secondary antibody responses to a synthetic Herpes peptide in mice in another series of experiments described in Example II below, showing the response in (B6×3CH)F1 mice to a conjugate of anti-I-A^(k) antibody, avidin and herpes peptide, both with (left hand curves) and without (right hand curves) priming with Freund's Complete Adjuvant;

FIG. 5 contains graphical representations of secondary antibody responses to streptavidin and avidin in mice in a yet further series of experiments described in Examples V below, showing the response in (B6×C3H)F1 mice (open squares) and B6 mice (closed squares) to a conjugate of anti-I-A^(k) antibody and steptavidin, when assayed against steptavidin (left hand curves) and avidin (right hand curves); and

FIG. 6 contains graphical representations of antibody responses to avidin in mice in one more series of experiments described in Example VI below, showing the response in C3H(H-2^(k)) mice (left hand upper and lower curves) and B6 (H-2^(b)) mice (right hand upper and lower curves) to a conjugate of anti-K^(k) antibody and avidin, both pre-boost (upper curves) and post-boost with avidin (lower curves).

DESCRIPTION OF INVENTION

In the present invention, an antigen, against which it is desired to raise antibodies in the body, is coupled or bonded to a monoclonal antibody, which is specific for a particular surface structure of antigen-presenting cells. This arrangement allows for a concentration of the antigen to the relevant cells in the immune system upon injection of the coupled material. The derivatised antibody, therefore, acts as a "vector" or "delivery vehicle" for targeting antigenic determinants onto the macrophage cells and B-cells, thereby facilitating their recognition by the T-helper cells. The presenting cells possess a variety of specific cell surface structures or markers which are targeted by the particular monoclonal antibody. Thus, antigens may be coupled to a monoclonal antibody specific for any of the surface structures on the antigen presenting cells, including Class I and Class II MHC gene products.

The surface structures on the antigen presenting cells of the immune system which can be recognized and targeted by the monoclonal antibody portion of the immunoconjugate are numerous and the specific such surface antigen structure targeted by the monoclonal antibody depends on the specific monoclonal antibody.

The monoclonal antibody may be provided specific for a gene product of the MHC, and, in particular, may be specific for class I molecules of MHC or for class II molecules of MHC. However, the invention is not limited to such specific surface structures and the conjugates containing the corresponding monoclonal antibodies but rather, as will be apparent to those skilled in the art, the invention is applicable to any other convenient surface structure of antigen presenting cells which can be recognized and targeted by a specific monoclonal antibody to which an immunogenic molecule is conjugated.

For example, as set forth in the Examples below, strong adjuvant-independent serological responses to a delivered antigen have been obtained with conjugates formed with dendritic cell-specific monoclonal antibody and CD4 cell-specific monoclonal antibody. In fact, for the latter monoclonal antibodies responses to the delivered antigen of about 10 to 20 fold greater than observed for the anti-class II MHC antibodies.

In the present invention, the monoclonal antibody specific for the target structure is provided in the form of a conjugate with an antigen against which it is desired to elicit an immune responses. The invention is particularly useful with antigen molecules which normally posses a weakly-immunogenic response, since that response is potentiated by the present invention. The antigen molecule may be in the form of a peptide or protein, as discussed above, but is not limited to such materials. Antigenic carbohydrates and other antigenic materials may be employed.

The terms "conjugate" as used herein are employed in their normal sense that the two molecules are joined together in some convenient manner to provide a stable structure suitable for in vivo administration.

The molecules may be joined together to form the conjugate by bonding using techniques known to those skilled in the art, with the bonds being of any suitable structure, including covalent bonding or affinity bonding.

One specific example of a conjugate useful in the present invention is that of the antigenic protein avidin and the monoclonal antibody specific for the I-A^(k) Class II major histocompatibility determinants. It is understood that this example is but one application of the general principle of the present invention discussed above. The preparative procedures described below are illustrative for the specific conjugate. The general principles of such procedures, however, may be employed to provide conjugates of any desired antigenic molecule and any desired monoclonal antibody to provide the desired antigen-antibody conjugate molecule for in vivo administration to achieve the desired adjuvant-independent serological response.

DESCRIPTION OF SPECIFIC ILLUSTRATIVE EMBODIMENTS

In this specific illustrative example, monoclonal antibodies specific for the I-A^(k) Class II major histocompatibility determinants may be prepared from a suitable hybridoma cell line. To permit easy conjugation with other proteins, the monoclonal antibodies preferably are biotinylated, prior to exposure to the appropriate protein antigen, in this example avidin. Avidin binds with high affinity to the biotinylated antibody, and has previously been characterized as an antigen. Varying doses of this conjugate were used to treat a strain of mice expressing the I-A^(k) determinants. Mice of a different strain expressing only I-A^(b) determinants were used as controls. The results of these experiments, given in detail in the Examples below, showed that avidin, when presented as an antigen in this manner (i.e. conjugated to the Mab to I-A^(k) Class II MHC) and in very low quantities can be made highly immunogenic in the absence of a standard adjuvant. If equivalent quantities of free avidin were mixed with non-biotinylated antibody (so that no conjugation occurred), no antibody response was elicited, indicating that the result was conjugate dependant. Recognition of the I-A^(k) determinants was essential, since avidin conjugated to an antibody of irrelevant specificity was not effective in eliciting an antibody response. In other experiments, also detailed in the Example below, a monoclonal antibody that is specific for the Class I MHC conjugated to avidin also showed an immunogenic response and generated antibodies to avidin. In additional experiments, considerably further enhanced antibody response was obtained using a dendritic cell-specific monoclonal antibody and a CD4 specific monoclonal antibody.

The conjugates which are employed in the present invention are not limited to conjugates of a single antigen with the monoclonal antibody but include conjugates where two or more antigenic proteins or peptides are conjugated to the monoclonal antibody, to provide a multivalent conjugate which can elicit an antibody response to each of the conjugated antigens.

A specific examples, biotinylated monoclonal antibody may be conjugated to avidin and bovine serum albumin or to avidin and a Herpes synthetic peptide. These conjugates were formed and used to immunize mice. The Herpes peptide is part of the Herpes simplex virus glycoprotein D. In these experiments, reported in detail in the Examples below, it was found that antibodies were raised against bovine serum albumen and the Herpes peptide, as well as against the avidin when the respective conjugates were tested. Replacement of the avidin by another protein, namely streptavidin, which also has high binding affinity to biotin, provided a good response, indicating that the targeting effect is not restricted to avidin and that there was no serological cross-reaction of anti-streptavidin antibodies with avidin.

It has also been shown in experiments reported in the Examples below that the response of mice to cumulative injections of a conjugate consisting of antibody-avidin-peptide is equivalent to the response using Freund's complete adjacent. This latter experiment indicates that vaccines can be constructed using peptide antigens that elicit antibodies that can be neutralising and protective against the pathogen from which the peptide is extracted without the necessity for adjuvants.

It is evident from the above that the invention may be used as a method of immunization in vivo and in vitro for making hybridomas, and thus specific monoclonal antibodies. Such specific antibodies have a wide range of use both in medicine and immunology.

In the following specific Examples, the efficacy of the invention is demonstrated for three immunologically-unrelated protein antigens, namely avidin, streptavidin and bovine serum albumin. In addition, the use of the method resulted in generation of IgG antibodies against a synthetic peptide from the glycoprotein D of herpes-simplex virus. In addition, an immunogenic response has been achieved using MAbs against Class I and Class II determinants of HMC, dentritic cells and CD4 markers. This data demonstrates the generality of the invention in application to the use of any conjugate of an antigen and a monoclonal antibody specific for surface structures on APC.

EXAMPLES Example I

This Example illustrates the preparation of biotinylated monoclonal antibodies and conjugates thereof with avidin.

Hybridoma cell lines TIB-92 (anti-I-A^(k)) and HB-65 (anti-influenza A NP, the control antibody) were obtained from the American Type Culture Collection (ATCC) Rockville, Md. U.S.A. and were cultured in RPMI 1640 culture medium, supplemented with 10% fetal calf serum, L-glutamine and antibiotics. The antibodies produced by these cell lines are both of the IgG2a subclass, and were purified from culture supernatants by conventional protein A-Sepharose chromatography.

The purified antibodies then were biotinylated using the general method described by Goding in "Monoclonal Antibodies: principles and Practice" (1983) Academic Press, London. For this method, the antibodies were dialysed against 0.1M sodium bicarbonate solution at pH 8.2, and concentrated to 1.0 mg/ml immediately before use. Biotin succinimide ester (Sigma Chemical Co.) was dissolved in dimethyl sulphoxide to a concentration of 1 mg/ml, immediately before use. 60 μl of this ester solution were added per ml of antibody solution at room temperature and left for 1 hour. The biotinylated protein was dialysed overnight against phosphate buffered saline (PBS) and stored at 4° C.

The biotinylated antibody prepared as just described was mixed with avidin in a ratio of 2 moles of antibody to 1 mole of avidin to form a biotinylated antibody-avidin conjugate for each of the antibodies.

Example II

This Example illustrates the immunogenic response of the conjugates prepared as described in Example I in mice.

Two different strains of mice (namely (B6×C3H)F₁ and B6 in groups of three were injected with the conjugates prepared as described in Example I as well as a mixture of antibody and avidin and of avidin alone according to the schedule contained in the following Table I:

                  TABLE I                                                          ______________________________________                                         Immunization Protocol                                                                                Priming Avidin                                                                              Adjuvant                                    Group  Priming Antigen                                                                               dose (μg) (FCA)                                       ______________________________________                                         I      (bio-anti-I-A.sup.k)-                                                                          5           --                                                 Avidin*                                                                        (bio-anti-I-A.sup.k)-                                                                         50           --                                                 Avidin*                                                                 II     anti-I-A.sup.k + Avidin                                                                        5           --                                                 anti-I-A.sup.k + Avidin                                                                       50           --                                          III    (bio-anti-NP)-  5           --                                                 Avidin+                                                                        (bio-anti-NP)- 50           --                                                 Avidin+                                                                 IV.    Avidin          5           +/-                                                Avidin         50           +/-                                         ______________________________________                                          Notes:                                                                         * = Biotinylated                                                               + = In Group III, antigen was injected only into (B6 × C3H)F.sub.1       mice                                                                           NP = nucleoprotein                                                             FCA = Freund's complete adjuvant                                         

The injections consisted of subcutaneous inoculations of 0.2 ml of the various solutions and after 21 days mice in all the groups were boosted with an intraperitoneal injection of 5 ug of avidin in 0.2 ml of PBS. Nine days later the mice were bled from the retro-bulbar sinus and their sera stored at 4° C.

The immune sera were tested for anti-avidin activity as follows: Avidin solution (50 μl) at a concentration of 20 μg/ml was added to the wells of a polyvinyl microtitre plate and incubated for 1 hour, after which the plates were washed. The plates then were incubated with a 1% solution of bovine serum albumin (BSA) in PBS for an additional 1 hour. The BSA-buffer was removed and 50 μl of serial dilutions of the immune sera in 1% BSA-PBS were added to each well and incubated for 1 hour. The plates were then washed three times with 1% BSA-PBS and then each well treated with 50 μl of ¹²⁵ I-protein A for 1 hour. The plates then were washed twice with buffer and the individual wells counted in a gamma counter.

The anti-avidin response of immune sera were plotted graphically and appear as FIG. 1. In this FIG. 1, the anti-avidin responses of the immune sera from groups I, II, III and IV (Table I) respectively are shown in A, B, C and D. The open circle line is the response in (B6×C₃ H)F₁ mice while the closed circle line is the response in B6 mice.

As may be seen from the data presented in FIG. 1, at the 5 μg dose of avidin, a significant response was observed in (B6×C₃ H)F₁ mice injected with (anti-I-A^(k))-avidin conjugate (FIG. 1A, open circles) whereas the B6 mice (FIG. 1A, closed circles), which do not have the particular surface antigens for which the antibody was made, were not appreciably sensitized (see FIG. 1A). This result cannot be attributed to an immuno-stimulating effect of the antibody alone, since the mixture of 5 μg of avidin with unmodified anti-I-A^(k) MAb did not elicit a response (FIG. 1B). An equal amount of avidin coupled to the control anti-NP MAb also failed to generate an appreciable response (FIG. 1C), indicating that the positive response shown in FIG. 1A is due to more than a simple conjugation of avidin to an antibody. As expected 5 μg of avidin injected with Freund's complete adjuvant induced a strong serological response (FIG. 1D). At the 50 μg of avidin dose, free avidin in the absence of adjuvant failed to stimulate a response (FIG. 1B), but in the form of (bio-anti-I-A^(k))-avidin, the conjugate sensitized both (B6×C3H)F₁ and B6 mice (FIG. 1A). Responses in the B6 mice are likely a reflection of the elevated reactivity of the avidin-MAb conjugate on the B6 targets and may be attributed either to cross-reactivity of the conjugated MAb or more efficient APC uptake of the MAb-avidin complex.

These results demonstrate that a low dose of avidin (i.e., 5 μg) can be made immunogenic in the absence of adjuvant when presented to the immune system coupled to a monoclonal antibody specific for recipient class II major histocompatibility determinants, namely the anti-I-A^(k) MAb.

The test procedure was repeated using a different anti-Class II MAb, in this case an anti-I-E^(k) as the targeting MAb. The results obtained were plotted graphically and are reproduced in FIG. 2. As may be seen therein, individual (B6×C3H)F₁ mice (open squares) immunized with the (anti-I-E^(k))-avidin conjugate gave a 7 to 9 fold higher response than the B6 mice (closed squares) that received the same dosage of conjugate. Unconjugated mixtures of avidin and the MAb gave only background levels of reactivity and this data is not presented.

Example III

This Example illustrates the use of antibody-biotin-avidin conjugates to raise antibodies to a third party protein.

A conjugate of anti-I-A^(k) antibody, avidin and bovine serum albumin (BSA) was formed by mixing equimolar amounts of biotinylated monoclonal antibody (prepared as described in Example 1), avidin and biotinylated bovine serum for 20 minutes at 20° C. The mixture then was centrifuged for five minutes at 12,000 g to remove any precipitable aggregates. Mice were injected subcutaneously with this complex (approx. 30 μg, BSA) in a similar regime to those in Example II, and, after three weeks, were boosted with an intraperitoneal injection of 10 ug of free BSA in PBS. Sera from the mice were obtained nine days later and assayed in a manner similar to the samples in Example II. The blocking buffer in the radioimmune assay contained 0.1% ovalbumin in PBS and 65,000 cpm of ¹²⁵ I-Protein A were added to each assay well.

The results obtained were plotted graphically and appear as FIG. 3. The open circle lines define the response in individual B3×C₃ H)F₁ mice while the closed circle lines represent the response in B6 mice. No response was observed in mice injected with an equivalent dose of avidin in an unconjugated mixture of non-biotinylated Mab and avidin and this data is not presented. As may be seen in FIG. 3, a considerable response to bovine serum albumin was observed. These data indicate the practicality of obtaining a serological response to any third party protein simply by coupling it to the MAb-Avidin complex. This would allow for the preparation of any number of adjuvant free subunit protein vaccines, that would avoid problems connected with the parent organism of the subunit protein.

Example IV

This Example illustrates the use of antibody-biotin-avidin conjugates to raise antibodies to a small peptide.

A biotin mediated conjugate was made between anti-I-A^(k) and avidin to which the Herpes synthetic peptide was coupled. The Herpes peptide used was an N-terminal peptide (12-20) from glycoprotein D of Herpes simplex virus and was photocoupled to avidin using the benzoyl-benzoyl-glycine linker moiety with a molar ratio of the peptide to avidin of 8:1. The peptide was synthesized and consisted of nine amino acids. After a course of three weakly injections of 30 ug of the anti-I-A^(k) -avidin-peptide conjugate into (B3×3H)F₁ mice, the mice were boosted once with avidin-(herpes peptide) intraperitoneally and then sera were collected nine days after the booster injection. The results are shown in FIG. 4. The illustrated results represent the net antibody response to Herpes peptide after subtracting the binding on the control samples and compared to the response obtained with a single priming in Freund's complete adjuvant (FCA) followed by the same booster injection.

EXAMPLE V

This Example illustrates the use of antibody-biotin-streptavidin complexes to raise antibodies to streptavidin.

Streptavidin is a protein which was extracted from Streptomyces avidinii. This protein material was conjugated with the anti-I-A^(k) biotinylated antibody following the procedure generally described above in Example I and the conjugate was injected into (B6×C3H)F₁ and B6 mice, in the manner described in Example II. Sera from these mice responded to streptavidin but were negative when assayed against avidin. These results appear graphically for individual mice in FIG. 5.

These results show that the targeting effect is not restricted to avidin, but is obtained with another serologically non-cross biotin-binding active protein.

Example VI

This Example illustrates the enhancement of avidin immunogenicity using monoclonal antibodies specific for Class I MHC's.

Using a method similar to Example I, avidin was coupled to biotinylated anti-K^(k) monoclonal antibody. This material (30 ug) was used to prime female C3H (H-2^(k)) or B6 (H-2^(b)) mice. Three weeks later the mice were bled to obtain preboost sera and then subsequently were boosted with avidin. The results appear in FIG. 6. As may be seen therein the C3H mice (open triangles) gave a higher anti-avidin response than B6 mice (closed triangles), indicating that there was specific delivery of avidin only in mice expressing the K^(k) determinants. These results illustrate that it is possible that any monoclonal antibodies directed against APC determinants can mediate antigen delivery even when these determinants are not restricted only to APC.

Example VII

This Example illustrates the enhancement of avidin immunogenicity using monoclonal antibodies specific for differing antigen-presenting cell surface makers.

Following the procedures generally described in the above Examples, experiments were conducted to compare the adjuvant-independent serological responses obtained to the protein antigen avidin when conjugated to different biotinylated monoclonal antibodies and injected in saline into mice.

Monoclonal antibodies specific for different cell surface makes were purified by affinity chromatography on Protein G-Sepharose (trademark) from their respective cell culture supernatants (all cell lines were obtained from ATCC).

The purified antibodies were biotinylated by reaction with an N-hydroxysuccinimide derivative of biotin and then conjugated to monovalent avidin, made functionally monovalent by adding biotin to fill three out of four biotin binding sites in the tetramer. The conjugates between the different biotinylated antibodies and monovalent avidin were formed by mixing the two components at equimolar ratios.

Three different mice strains, namely C3H(-2^(k)), C57B1/6(H-2^(b)) and (C3H×C57B1/6F1(H-2⁵ ×H-2^(k)), wee injected with the different immunoconjugates according to an immunization protocol of a single subcutaneous injection with the immunoconjugate (containing 10 ug of avidin), followed 3 weeks later by a single intraperitoneal boost with 10 ug of avidin only in saline. Mice were bled 1 week post-boost and the sera analyzed for avidin-specific 1 gG responses.

The responses observed for the different immunotargeting antibodies are set forth in the following Table II, as arbitrary units of response in an enzyme-linked immunoassay relative to a standard curve established with a monoclonal anti-avidin antibody.

                                      TABLE II                                     __________________________________________________________________________                                  ANTI-AVIDIN ANTIBODY                              TARGETING                    RESPONSE (arbitrary units/ml)                     ANTIBODY                                                                               SPECIES                                                                              SUBCLASS                                                                              SPECIFICITY                                                                            F1    B6   C3H                                    __________________________________________________________________________     TIB 92  MOUSE IgG2a  I-A(k)  17.28*                                                                               0.77 1.21                                   HB 26   MOUSE IgG2a  I-A(b)  11.88*                                                                               0.53 2.37                                   TIB 227 RAT   IgG2b  DENDRITIC                                                                              228.24*                                                                              13.39*                                                                              43.71                                  TIB 128 RAT   IgG2b  MAC-1   2.43  5.65*                                                                               5.83                                   TIB 166 RAT   IgG2a  MAC-2   1.02  <0.09                                                                               1.15                                   TIB 163 MOUSE IgG1   B cells 4.47* 0.27 0.24                                   TIB 164 RAT   IgG2b  B cells 20.52*                                                                               0.81 1.29                                   TIB 207 RAT   IgG2b  CD4     125.92*                                                                              16.24*                                                                              N/D                                    TIB 105 RAT   IgG2a  CD8     9.33* 0.81 N/D                                    HB 65   MOUSE IgG2a  NP.sup.(1) (flu)                                                                       0.42**                                                                               0.32**                                                                              0.22                                   PBS                  --      0.03  3.48 N/D                                    FCA                  --      14427.7                                                                              2865.34                                                                             3322.58                                __________________________________________________________________________      *significantly different from **                                               N/D not done                                                                   .sup.(1) Control antiinfluenza nucleoproteinavidin conjugate             

As expected from the findings reported in the previous Examples, the two anti-class II major histocompatibility complex antibodies (anti-I-A^(k) and anti-I-A^(b)) promote significant responses in the (C3H×B6) F1 animals, reflecting allele specific immunotargeting.

In addition, two other antibodies promoted strong adjuvant-independent serological responses, namely the dendritic specific monoclonal antibody T1B 227 and the monoclonal antibody T1B 207 recognizing the CD4 marker in the mouse. The immune response observed for these two antibodies is approximately 10 to 20 fold greater than that observed for the anti-Class II MHC antibodies.

The data presented in this Example serve to illustrate that immunospecific targeting of a protein antigen to both MHC and non-MHC surface markers or cells in the immune system promotes strong adjuvant-independent serological responses to the delivered antigen.

SUMMARY OF DISCLOSURE

In summary of this disclosure, the present invention provides a novel method of vaccinating mammals by the conjugation of antigens, which may be in the form of synthetic epitopes or protein subunits to monoclonal antibodies specific for antigen-presenting cells of the recipient, such that these antigen-antibody conjugates may be used to elicit a beneficial antibody response without needing to use deleterious adjuvants. Modifications are possible within the scope of this invention. 

What we claim is:
 1. A novel conjugate physiologically suitable for administration to a mammal to elicit an immune response, comprising at least one antigen which is a peptide or protein against which an immune response is to be elicited conjugated to a monoclonal antibody specific for a surface structure of antigen-presenting cells of the mammal.
 2. The conjugate of claim 1, wherein different tandemly linked antigen molecules are bonded to said monoclonal antibody, to elicit an immune response to each of said antigen molecules upon administration.
 3. The conjugate of claim 1 wherein said antigen is a weakly-immunogenic peptide or protein.
 4. The conjugate of claim 1 wherein said monoclonal antibody is specific for dendritic cells.
 5. The conjugate of claim 1 wherein said monoclonal antibody is specific for CD4.
 6. The conjugate of claim 3 wherein said weakly-immunogenic molecule is a synthetic peptide comprising an amino acid sequence to the epitope of an antigen molecule of a pathogen.
 7. The conjugate of claim 3 wherein said weakly-immunogenic molecule comprises an epitope of the protein sub-unit of a pathogen.
 8. A vaccine physiologically suitable for administration to a mammal to elicit an IgG antibody response to an antigen, which consists essentially of a conjugate comprising at least one normally weakly-immunogenic antigen which is a peptide or protein against which the IgG antibody response is to be elicited conjugated to a monoclonal antibody specific for surface structures of antigen-presenting cells of the mammal and suitable carrier therefor, whereby said antibody response occurs without an immunogenicity-enhancing adjuvant.
 9. The vaccine of claim 8 wherein said weakly-immunogenic peptide is a synthetic peptide comprising an amino acid sequence to the epitope of an antigen molecule of a pathogen.
 10. The vaccine of claim 8 wherein said weakly-immunogenic protein is an epitope of protein subunit of a pathogen.
 11. The vaccine of claim 8, wherein said monoclonal antibody is specific for dendritic cells.
 12. The vaccine of claim 8, wherein said monoclonal antibody is specific for CD4.
 13. A method of immunization of a mammal against a pathogenic disease by the administration to the mammal of at least one antigen which is a peptide or protein and which elicits an antibody response to said pathogenic disease, which comprises administering said antigen in the form of a conjugate wherein said antigen is conjugated to a monoclonal antibody specific for surface structures of antigen-presenting cells of the mammal.
 14. The method of claim 13 wherein said conjugate comprises different tandemly linked antigen molecules so as to elicit an immune response to each of said antigenic molecules.
 15. The method of claim 13 wherein said antigen is a weakly immunogenic peptide or protein whose immunogenicity is significantly enhanced by said conjugation to said monoclonal antibody, whereby said IgG antibody response to said antigen is achieved in the absence of immunogenicity-enhancing adjuvants.
 16. The method of claim 13, wherein said monoclonal antibody is specific for dendritic cells.
 17. The method of claim 13, wherein said monoclonal antibody is specific for CD4.
 18. The method of claim 15 wherein said weakly-immunogenic peptide or protein is a synthetic peptide comprising an amino acid sequence to the epitope of an antigen molecule of the pathogenic organism.
 19. The method of claim 15 wherein said weakly-immunogenic peptide or protein is a subunit protein comprising an epitope of an antigen protein molecule of the pathogenic organisms. 